(a) Technical Field
The present invention relates to an operation control method of a fuel cell and more particularly, it relates to an operation control method of a fuel cell, which extends the operation field of the fuel cell in a fuel cell electric vehicle and ensures power performance in the initial stage of starting the vehicle.
(b) Background Art
A fuel cell is a type of power generating device that does not convert chemical energy of a fuel into heat by combustion, but converts the chemical energy into electrical energy by an electrochemical reaction within a stack. Fuel cells are used to provide electric power for a small electric/electronic product, particularly a portable device, as well as provide electric power for industry, household, and vehicle driving. Among the fuel cells, a polymer electrolyte membrane fuel cell (PEMFC) also known as a proton exchange membrane fuel cell is currently used as a power supply source for driving vehicles.
The PEMFC has characteristics of low operating temperature, high efficiency, high current density and output density, short starting time, and rapid response to load change, as compared with the other types of fuel cells. Thus, the PEMFC can be widely used as a power source for vehicles or portable devices.
The PEMFC includes a membrane electrode assembly (MEA) in which catalyst electrode layers causing electrochemical reactions are attached to both sides of a polymer electrolyte membrane through which hydrogen ions move, a gas diffusion layer (GLD) that uniformly distributes reaction gases and transfers generated electrical energy, a gasket and a coupling mechanism for maintaining air-tightness of the reaction gases and coolant and appropriate coupling pressure, and a bipolar plate that moves the reaction gases and the coolant.
A fuel cell system applied to fuel cell electric vehicles includes a fuel cell stack configured to generate electric energy by an electrochemical reaction of reaction gases (e.g., hydrogen as a fuel and oxygen as an oxidizer), a hydrogen supply device configured to supply hydrogen as a fuel to the fuel cell stack, an air supply device configured to supply air including oxygen to the fuel cell stack, a heat and water management system configured to adjust the operation temperature of the fuel cell stack and perform a water managing function, and a fuel cell controller configured to operate the fuel cell system.
In a typical fuel cell system, a hydrogen supply device includes a hydrogen storage (e.g., hydrogen tank), a regulator, a hydrogen pressure control valve, a hydrogen recirculation device, and the like. An air supply device includes an air blower, a humidifier, and the like. A heat and water management system includes a coolant pump, a water tank, a radiator, and the like.
Meanwhile, fuel cells have characteristics that optimum performance appears in the range of specific cell temperature and supply gas relative humidity. For a PEMFC, the operation is possible in a temperature range of 0 to 80° C., but its output performance is limited at an appropriate operation temperature or less. When the fuel cell is used as a power supply source of a vehicle, there is a limitation in satisfying sufficient power performance required in acceleration when the operation temperature is relatively low in the initial stage of starting. Particularly, when remaining formation water exists in a cell of the fuel cell when the vehicle is left after starting of the vehicle is stopped, access of fuel gas (e.g., hydrogen) to a reaction portion of the cell may be limited due to the remaining formation water in the starting of the vehicle.
In particular, when a current output is continuously requested to supply power to the vehicle, a severe load is applied to the cell of the fuel cell, and therefore, performance degradation may occur. When the supply of hydrogen to an anode electrode is deficient, the potential of the anode electrode rapidly increases, and therefore, a specific cell voltage may have a ‘−’ value, that is, a negative value. In other words, a reverse voltage may be generated. Accordingly, in a fuel cell electric vehicle, a fuel cell system and the vehicle are operated in such a manner that a cell of a fuel cell is protected by performing current limitation for artificially limiting an output current when the cell voltage of the fuel cell is less than a setting voltage as the cell voltage is monitored.
FIG. 1 is a flowchart illustrating a conventional process of performing current limitation according to the related art. During normal operation of a fuel cell (e.g., operation without error) (S1), a controller is configured to monitor a cell voltage (S2). When the cell voltage is less than a setting value, current limitation is performed (S3 and S4). This is a control strategy required in terms of securing durability by protecting a cell of the fuel cell. However, the merchantability of a vehicle may deteriorate due to deficiency of power performance of the vehicle in the initial stage of starting, particularly in low temperature starting.
In addition, a process of removing moisture by excessively operating an air blower should be performed to remove removing formation water in the cell after starting of the vehicle is stopped, which causing noise to be generated when the starting of the vehicle is stopped. A developed method in the related art discloses a technique for adding an oxygen evolution catalyst (OEC) (water electrolysis catalyst) to an anode electrode catalyst for a hydrogen oxidation reaction to prevent carbon corrosion of an anode electrode and protect the anode electrode in the generation of a reverse voltage.
However, the addition of the OEC is focused on the security of durability in terms of the material of an electrode. Therefore, there has been proposed no operation control strategy for extending the operation field of a fuel cell or ensuring power performance in the initial stage of starting in a vehicle including the fuel cell with improved reverse voltage durability to which the corresponding electrode is applied.